This application is related to co-pending application U.S. Ser. No. 10/006,327, filed concurrently herewith.
The present invention relates in general to a rear subframe for a multi-link vehicle suspension, and, more specifically, to increasing stiffness of the subframe using tension/compression struts.
The vehicle frame supports the vehicle body and, together with other components, such as control arms, springs, and shock absorbers, comprises the suspension system which permits up and down wheel movement without up and down movement of the body. Due to the many forces to which the frame is subjected, it is important that the frame have high stiffness for purposes of structural integrity, vehicle geometry, and creation of noise.
The vast majority of vehicle frames have been fabricated from steel because of its high strength, high stiffness, and reasonable cost. However, there are also concerns for minimizing the weight of a frame, based mainly on a desire to improve fuel economy.
Integral castings of aluminum or aluminum alloys may be used as vehicle frames or more typically subframes, cradles, and cross members (i.e., frame sections). Aluminum is able to provide good stiffness and can provide a significant reduction in weight. A hollow cross section (e.g., box or tubular) of the subframe members is used to further improve stiffness and reduce weight.
Although the characteristic stiffness of aluminum or aluminum alloy is good, the e-module or longitudinal stiffness is about three times less than it is for steel. Therefore, the aluminum casting has to maintain a certain thickness in order to maintain sufficient stiffness, thus limiting the amount of weight reduction that could be obtained in the prior art.
The present invention has the advantage of increased stiffness of a vehicle frame while minimizing the thickness of the main aluminum casting, resulting in further improvement of weight reduction while simultaneously achieving a desired amount of stiffness.
In one aspect of the present invention, a frame apparatus for a vehicle comprises an aluminum subframe including a substantially hollow left side-rail, a substantially hollow right side-rail, a front cross-member, a rear cross-member, a left-side upper control arm attachment, a left-side lower control arm attachment, a right-side upper control arm attachment, and a right-side lower control arm attachment. The substantially hollow side-rails and cross-members each has a respective cross-sectional diameter over a majority of their respective lengths about equal to a first predetermined diameter. A tension/compression strut element has a first end and a second end, the first and second ends being affixed between a first locus and a second locus on the cast aluminum subframe. The tension/compression strut element has a substantially straight body between the first and second ends and has a respective cross-sectional diameter over a majority of its substantially straight body about equal to a second predetermined diameter, the second predetermined diameter being less than about one-half of the first predetermined diameter.